In the majority of angiosperms, during the seed development, after fertilization, reserves accumulate in a particular tissue, called endosperm, which is generally triploid.
The endosperm will provide the embryo for feeding. It results from the fusion of one of the two spermatic nuclei (male) with both polar nuclei of embryo sac (female).
This endosperm divides very actively, but in a very peculiar manner; nuclei are not separated by cell walls, but are placed on the periphery of the embryo sac forming a coenocytic mass, which covers sac walls and progresses little by little towards inside.
Later on, and depending on species, this mass will or not segment and transform into a true cellular tissue. In the embryo sac, the embryo develops, from globular state to its final state through various intermediate states, which depend on the species (e.g. in melon: cordiform then torpedo and finally cotyledonous states). In the meantime, endosperm grows at the expense of nucellus, which resorbs progressively, in such a way that in mature seed, endosperm gets in direct contact with teguments.
But in some cases, endosperm disappears progressively and reserves accumulate then into cotyledons which become thicker and puffed, and fill in all the seed.
The seed is then designated as "non endospermic". This type of seed is met in numerous botanical families, as Cruciferae (e.g. brassicas, rape seed), Papillonaceae (e.g. legumes as bean, pea, soyabean), Cucurbitaceae (e.g. melon, cucumber, squash), Compositae (e.g. sunflower).
In opposite, cereals (including maize), solanaceae, and many other cultivated plants have endospermic seeds. In endospermic seeds, reserves which remain within endosperm instead of accumulating into cotyledons are directly mobilized from endosperm during germination process.
It is already known that physicochemical gradients inside endosperm (Ryczkowski, 1967) and nutrients provided to the embryo (Monnier, 1980) are decisive for a normal morphogenetic expression which will lead to autotrophy.
It has also been demonstrated that chemically induced mutations affecting endosperm development could result in a more or less strong embryo lethality in maize (Neuffer and Sheridan, 1980) or in Arabidopsis (Meinke, 1985).
It is also known that, in higher plants, there are a large number of genes expressed during the male gametophytic phase (i.e. the haploid development phase in which male reproductive cells called "male gametes" differentiate). A large portion of these genes are also expressed in the sporophytic phase (i.e. the phase corresponding to the diploid development till the next gametophytic phase, of the organism issued from a zygote--or egg--which results from the fusion of male and female gametes during fertilization) (Mascarenhas et al. 1986).
It has also been observed that components of pollen development and function show positive correlations with endosperm development (Mulcahy 1971, Ottaviano et al., 1980), and that some alleles determining defective endosperm in maize (Ottoviano et al. 1988) and lethal embryo in Arabidopsis (Meinke 1982, 1985, Meinke and Baus 1986) are expressed in the male gametophyte. In this last case, the detection of defective endosperm mutant genes affecting the male gametophytic generation is mainly based on distortion from the expected mendelian segregation, and on heterogeneity between ovary sectors.